Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Nellie has extremely high liver and kidney enzyme levels, has a bloated abdomen, and is shaking and refusing to eat for you.
I think that your veterinarian's plan of an abdominal ultrasound is exactly what the next step should be. That will allow them to evaluate her entire abdomen, and take aspirates and/or biopsies of any organs that don't appear normal and if present fluid accumulating in her abdomen for culture and analysis.
When we see multiple organs affected we do need to think of a systemic infection, such as a bacterial infection called Leptospirosis, or, unfortunately, cancer.
If you live in an area that has Leptospirosis I would start antibiotic therapy effective in treating that organism now, as the sooner treatment is started the better they respond. Most dogs do very well if the infection is caught early, they can make a full recovery.
In the meantime I highly recommend that Nellie be placed on intravenous fluids, an injectable antinausea drug like Cerenia, and an appetite stimulant (mirtazapine is a good one). They can also give antibiotics in injectable form so they don't interfere with her appetite.
Best of luck with your girl, please let me know if you have any further questions.